To transmit messages in secret.
Numbers are used in zip codes.
cypher codes
AnswerDelivery codes.
Device codes on televisions are used for communications between the television and the remote control. The codes are used to setup and change channels.
Any membership codes that are posted would have been used, and membership codes can only be used once.
E codes
e
Category III codes
You can't. only three codes were possible, And they were already used.
codes that can no longer be used
Game shark codes
Zip Codes are only used in the United States. There are no international zip codes.